Julie A. Wolin

Recent Changes in Lake Ontario 1981–1987: Microfossil Evidence of Phosphorus Reduction

Abstract Quantitative analysis of siliceous microfossils in a finely sectioned (0.5 cm) core of near-surface sediments from Lake Ontario indicates the lake is responding to reductions in phosphorus loading. The magnitude of response, however, is very small. Increased diatom accumulation and modified species composition indicates some relaxation of silica limitation, particularly in early spring. Abundance of some diatom species associated with grossly polluted areas of the Great Lakes has been reduced, but most recently deposited assemblages are composed of species tolerant of eutrophic conditions. No reappearance of species assemblages abundant in Lake Ontario prior to 1935 and presently associated with oligotrophic conditions in the upper Great Lakes were noted. Changes in species composition are consistent with observed recent changes in N:P ratio.

Late Holocene lake-level and lake development signals in Lower Herring Lake, Michigan

Paleolimnological investigations of a marginal lake in the Lake Michigan basin revealed signals of long-term lake-level changes primarily controlled by climatic forces. Multiple analyses identified concurrent signals in sediment chemistry, grain size, and the microfossil record. Coarse-grained sediments, benthic diatoms, and nutrient response species increased as lake levels rose or fell. Finer sediments and higher percentages of taxa associated with stable thermocline conditions occurred during high-lake periods. Sedimentary evidence revealed corresponding strong high-lake signals c. 2500–2200, 1800–1500, 1170–730, and 500–280 BP. Low-lake periods occurred c. 1500–1170 and 700–500 B.P. An additional signal of lake-level decline was apparent beginning c. 280 BP but was interrupted by anthropogenic effects. Evidence of extreme low-lake levels (c. 1400–1300 BP), and signals for a medieval warming period (1030–910 BP) and the Maunder minimum (370–325 BP) indicate occurrence of short-lived dry climatic conditions.

A multimetric index of lake diatom condition based on surface-sediment assemblages

Abstract.  We developed and evaluated a multimetric index of lake diatom condition (LDCI) based on surface-sediment samples for the National Lake Assessment (NLA) by the US Environmental Protection Agency. We selected final metrics in each of 5 categories for use in composite metrics of biological condition, which we combined in a hierarchical multimetric index. The final metrics selected for the LDCI had responses as predicted based on ecological principles, wide ranges, high signal-to-noise ratios, the ability to distinguish reference from disturbed lakes, and low intercorrelation. The final metrics were: Shannon diversity, taxon richness, % reference taxa, % tolerant taxa, % epiphytic individuals, % chain-forming individuals, % low-P taxa, % low-N taxa, % high-P taxa, % high-N taxa, % Achnanthidium individuals, % Cocconeis individuals, and % Cyclotella + Stephanodiscus individuals. We developed and tested models for adjusting the expected reference LDCI at a site for natural variation among sites. The best model used lake morphology, watershed attributes, and climate variables to predict expected reference LDCI for each lake. The adjusted LDCI was the observed LDCI at a lake minus the expected reference LDCI modeled for that lake. The adjusted LDCI varied less among reference sites than the LDCI, indicating the adjusted LDCI better accounted for natural variability among sites than the LDCI. However, it had less power than the LDCI to separate reference and disturbed lakes, a result attributed to lower values of expected reference LDCI in landscapes with high agricultural land use. The adjusted LDCI is the first multimetric diatom index developed for lakes, applied at a scale as large and diverse as the USA, and corrected for natural variation among lakes. According to the adjusted LDCI, 47.1% of USA lakes were in reference condition, 27.0% were in fair condition, and 23.2% were in poor condition.

The effect of dispersal ability in winter and summer stoneflies on their genetic differentiation

Abstract 1. Plecopteran species disperse less than most other aquatic insects. Within stoneflies, members of different families vary in the degree of wing morphology and season of adult emergence.